This application claims priority of United Kingdom patent application No. 0008038.2, filed Apr. 1, 2000.
The invention relates to a clamp bar for a sanding machine.
Sanding machines using a rotating cylindrical sanding drum are well known. An abrasive paper sheet or a screen is wrapped around the drum and held in place by a clamp bar which locates in a recess formed in the cylindrical surface and clamps the ends of the paper.
In order to avoid chatter, the recess is not quite parallel to the axis of the drum but advances circumferentially by about 20xc2x0 over its length. Because of this advance, the paper clamp bar must be formed to a helical shape to conform to the recess. In the prior art, the clamp bar is of constant thickness along its length and is very slightly concave from end to end on one side and very slightly convex on its other side. Thus, only the concave side can be correctly fitted to the drum and when this is worn out, due to abrasion between the drum and the bar during operation of the sanding machine, the clamp bar must be discarded. Because the concavity/convexity of the clamp bar is fairly slight, it is not uncommon for inexperienced operators to fit the clamp bar with the convex face against the drum instead of the concave face.
The present invention overcomes the disadvantages of the prior clamp bar by providing a clamp bar which has an identical concave surface on either side and can thus be fitted to the drum either way up.
Accordingly, the invention provides a paper clamp bar for a sanding machine, comprising an elongate bar having two opposed major faces each defined by a concave helical surface.